Yes, that's different! "Coffee grounds" is a very common indicatiuon of internal bleeding. When blood gets digested in the colon, it "balls up", changes color, and takes on that "coffee ground look."
If you are taking the ibuprofen on an empty stomach and doing it often or taking lots of it, thats your main culprit. Eat some food first to help "buffer it" if you must take it. Or maybe its the shells... how hard are they? I always get the shelled punkin seeds. Termites can digest lumber... but we cannot! I never was brave enough to try the shelled ones... they just looked too "hard" I guess.